(1) Field of the Invention
The invention relates to a method of manufacturing a tubular component, such as an inflatable bladder and/or elastomeric cover for subsequent use in a packing device for a subterranean well.
(2) Description of the Prior Art
Inflatable packers, bridge plugs, and the like, have long been utilized in subterranean wells. Such inflatable tools normally comprise an inflatable elastomeric bladder element concentrically disposed around a central body portion, such as a tube or mandrel. A sheath of reinforcing slats or ribs is typically provided exteriorally around the bladder with an elastomeric packing cover concentrically disposed around at least a portion of the sheath. Generally, the central portion of the sheath will remain exposed and without a cover for providing anchoring engagement of the packer to the wall of the well. Pressured fluid is communicated from the top of the well or interior of the well bore by means of a down hole pump to the interior of the body and thence through radial passages provided for such purpose or otherwise around the exterior of the body to the interior of the bladder during inflation.
Normally, an upper securing means engages the upper end of the inflatable elastomeric bladder and the reinforcing sheath (if included in the design), sealably securing the upper end of the bladder relative to the body, while a lower securing means engages the lower end of the bladder and reinforcing sheath, securing the lower end of the bladder for slidable and sealable movement relative to the exterior of the body, in response to inflation forces. An elastomeric cover may be secured to the exterior of the sheath or placed around the exterior of the bladder, in known fashion.
With inflatable packers of this type, it has been observed that the portion of the bladder adjacent to the exposed sheath section of the packer prematurely inflates prior to the other portions of the bladder which are reinforced against expansion by the reinforcing sheath and/or the elastomeric packing cover element. When an exposed portion, such as the exposed sheath section of the packer, expands, one end of the bladder moves toward the other end of the device, and the bladder area adjacent the exposed sheath inflates until it meets the wall of the well bore, which may be cased or uncased. If the well bore is uncased, the well bore will have an earthen wall, and if the well bore is cased, the wall of the well bore will be the internal diameter surface of the casing.
It has been noted in a number of prior art designs that when service conditions encompass moderate expansion ratios, a propensity for the bladder to pinch around the exterior of the body arises, creating either a seal or a convoluted fold in the bladder that sometimes prevents the effective communication of further fluid throughout the bladder and preventing contiguous inflation propagation. The pinching seal and/or fold(s) become entrenched in the bladder whereupon they obstruct further passage of fluid employed for inflating the bladder and therein keep fluid from reaching the farthest portions of the bladder to be inflated. When this occurs in service, it always results in a soft set condition and the imminent loss of seal between the cover and wellbore.
The formation of folds creates unusually high triaxial stresses and strains in the vicinity of the fold. Correspondingly, these triaxial stresses and strains create a condition that causes localized failure of the bladder by means of cracking and/or tearing. Failure occurs because the physical properties of the elastomeric material composing the bladder are not adequate to survive the service conditions, i.e., highly localized triaxial, the bladder is pressed with high magnitudes of force against the ribs, exposure to aggressive inflation and treatment fluids, elevated service temperatures, pressure transients, exposure to low aniline point hydrocarbons and acid gases and the like.
The ability to successfully deflate and retrieve an inflatable device is a common service requirement. A pinch or fold might still have formed in a bladder during inflation even though the inflation element effected a satisfactory seal against the wall of the well. During deflation, a fold can pinch and seal around the body, obstructing the transmission of fluid out of the lower portions of the bladder and thereby prevent complete deflation of the bladder. Once a fold is formed, it is permanently entrenched in the bladder and results in multiple layers of bladder beneath the ribs. These layers, in turn, result in a deflated diameter which is greater than the initial run-in diameter of the inflation element. Retrieval of the device to the earth""s surface is thus compromised since the device may not be able to pass through restrictions in the well bore as it is moved upwardly therein. These problems and some prior art solutions are discussed in Eslinger, et al., xe2x80x9cDesign and Testing of a High-Performance Inflatable Packer,xe2x80x9d Society of Petroleum Engineers Paper No. 3748 (1997).
In my U.S. Pat. No. 5,813,459 entitled xe2x80x9cProgrammed Shaped Inflatable Packer Device,xe2x80x9d issued Sep. 29, 1998, I disclose a method to abate the formation of pinching seals and folds during inflation of prior art devices by providing a series of shape-controlling means on an elastomeric packing cover along the length of the bladder in the form of high and low modulus modules of varying lengths and thicknesses. While this design is an advancement in the art, the design of the modules leaves comparatively sharp angles and significant size differences between the high and low modules. Sometimes these angles and different diameters are of such magnitude that they are easily detected by the naked eye. Additionally, in this prior art device, the thickness of intervals of the cover segments are programmed in concert with the exposed rib section(s) in an effort to control the transitional shapes taken by the inflation element throughout inflation. The bladder in this invention has a constant inside diameter (ID) and a constant outside diameter (OD), i.e., a constant thickness and cross section along its entire length. In such design the cover segments dominate and control the transitional shapes taken by the inflation element throughout inflation.
Prior art techniques of manufacturing bladders and covers for inflatable packing devices for use in subterranean wells have included extrusion methods and conventional mandrel wrapping methods. Bladders in prior art downhole tools have always been of constant ID, OD and thickness. Mandrel wrapped bladders have always been made on constant diameter mandrels except, very large bladders used in external casing packers are sometimes made on a mandrel with a very small draft angle to facilitate sliding removal of the bladder from the mandrel. For all practical intents and purposes the diameter of these mandrels are considered constant as are the thicknesses of the bladders made on these mandrels. Moreover, even this draft angle configuration on the mandrel does not result in providing a wall thickness program onto a tubular component.
Covers in prior art down hole tools have always been made by means of wrapping calendared elastomer onto the ribs of the inflation element or wrapping calendared elastomer onto a constant OD mandrel. Prior art devices having programmed thicknesses over intervals of the cover(s) have had their programmed thicknesses imparted via machining of the cover(s) after it has been bonded and cured on the ribs.
The invention provides a method of manufacturing a tubular component to permit transfer of a wall thickness program or orchestration of the varying sophisticated contours and configurations in the tubular component, i.e., the bladder and/or cover, to provide a uniform expansion profile in an expected, i.e., pre-determinable and repeatable, manner which can be achieved by those skilled in the art with only minimal or nominal experimentation which will be within the ordinary skills of those knowledgeable in the design and use of inflatable elastomeric devices for use in subterranean wells, and by adhering to the teachings herein.
The present invention provides a method of manufacturing a wall thickness program into an elastomeric tubular component which may thereafter be incorporated into a packing device for use in a subterranean well. The method comprises the steps of contouring upon a surface diametrical configuration which defines a wall thickness program for the tubular component. The diametrical configuration is transferred from the surface onto at least one of the inner or outer walls of the tubular component as a wall thickness program such that the transferred a diametrical configuration conforms substantially as a mirror image of the program on the contoured surface. The surface may be a rotatable mandrel and the contouring may be performed during rotation of the mandrel. In an embodiment of the present invention, a rotatable elongated mandrel is provided upon which an elastomeric tubular conduit is inserted. The diametrical configuration is contoured around either or both of the inner and outer diameters of the elastomeric tubular conduit, such as by machining upon the outer diameter of the conduit, and/or by implacing the diametrical configuration first upon the rotatable elongated mandrel and contouring such configuration by transfer through hydrostatic compression between the mandrel and the tubular conduit within an autoclave through application of heat. In one embodiment, the present method comprises steps of first providing an elongated mandrel which, preferably, will be metallic, such as steel or the like, and will have an exterior surface which is at least substantially equal to the effective length of the desired tubular component to be manufactured. The surface of the elongated mandrel has an original outer diameter which is defined along the surface and may further include a terminal section portion at each end of the mandrel. A diametrical configuration is imparted onto the exterior of the mandrel between the terminal sections. Thereafter, the tubular elastomeric component is formed on the mandrel by wrapping a ribbon of calendared elastomer, in layers, around the mandrel as it is manipulated, such as by rotation, to provide an uncured tubular component having a specified outer diameter. Extrusion abating heat shrinkable tape thereafter is applied around each terminal section of the tubular component to retain the ends during curing. The tape is also wrapped around the OD of the uncured tubular component to apply a substantial hydrostatic compressive force to the tubular component around the mandrel. Curing of the tubular component onto the mandrel is effected by application of heat via steam and/or dry heat in an autoclave. The hydrostatic compressive force on the multiple elastomeric layers fuse to become one unit and thereby transfer the diametral configuration from the mandrel onto the tubular component. The contour of the cured tubular is also fused in place during the curing operation. The ID contour within the elastomeric tubular component become the reverse mirror image of the OD contour of the mandrel. Thereafter, the tape is removed from around the exterior of the tubular component and the tubular component is removed from the mandrel and installed into (or onto) the packing device in known fashion.
A variant of the method comprises the use of a constant outer diameter mandrel and machining the desired diametral configuration onto the outer diameter of the cured elastomeric tubular component.
There are many significant practical benefits afforded by this invention. It provides a repeatable, precise, quality assured, expedient way to manufacture elastomeric tubular with varying thicknesses along its length. This invention provides manufacturers with multiple methods of making elastomeric tubular intended to control or influence the transitional shapes taken by inflation elements throughout inflation.